Processing of low rank coal

ABSTRACT

A method of preparing a fuel composition includes placing coal having a heat content between about 3,000 BTU/lb and about 9,000 BTU/lb and a moisture content between about 20 wt % and about 60 wt % in a vessel. The coal is exposed to heat and a pressure less than atmospheric pressure within the vessel, thereby reducing the coal, such that an average primary particle size of the coal is less than 1 millimeter. A binder is introduced to the vessel, such that the coal combines with the binder to yield a mixture. The mixture is shaped to yield a fuel composition.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.17/150,904, filed Jan. 15, 2021, which claims the benefit of priority toU.S. Provisional Application No. 62/961,552 filed on Jan. 15, 2020, andentitled “PROCESSING OF LOW RANK COAL,” the contents of which are herebyincorporated by reference.

TECHNICAL FIELD

This disclosure relates to processing of low rank coal, such as lignite.

BACKGROUND

Low rank coal (e.g., lignite) is softer, is more CO₂ intensive, and hasa higher moisture content and lower fuel value than “hard” coal (e.g.,bituminous, sub-bituminous, anthracite). Lignite, the lowest rank coal,typically has a moisture content in a range of 30-60 wt % and a heatcontent in a range of 4,000-8,300 BTU/lb. In contrast, sub-bituminouscoal typically has a moisture content in a range of 10-45 wt % and anenergy content in a range of 8,500-13,000 BTU/lb, and bituminous coaltypically has a moisture content in a range of 2-15 wt % and a heatcontent in a range of 11,000-15,000 BTU/lb. Due to its high moisturecontent and brittle nature, processing of low rank coal requiressignificant energy input and results in the creation of coal fines(e.g., dust), which presents a combustion hazard and is of little use.

SUMMARY

Certain aspects of the subject matter described can be implemented as amethod or preparing a fuel composition. The method includes placing coalhaving a heat content between about 3,000 BTU/lb and about 9,000 BTU/lband a moisture content between about 20 wt % and about 60 wt % in avessel. The coal is exposed to heat and a pressure less than atmosphericpressure within the vessel, thereby reducing a primary particle size ofthe coal, such that an average primary particle size of the coal is lessthan 1 millimeter. A binder is introduced to the vessel, such that thecoal combines with the binder to yield a mixture. The mixture is shapedto yield a fuel composition.

This, and other aspects, can include one or more of the followingfeatures.

In some embodiments, the coal is exposed to heat before combining thecoal and the binder. In some embodiments, exposing the coal to heatincludes heating the coal by conduction. In some embodiments, exposingthe coal to heat includes contacting the coal with a heated surface. Insome embodiments, the heated surface includes a rotating blade.

In some embodiments, the coal is agitated in the vessel. In someembodiments, agitating the coal includes intermittently agitating thecoal in the vessel.

In some embodiments, exposing the coal to the pressure less thanatmospheric pressure within the vessel includes intermittently reducingthe pressure in the vessel.

In some embodiments, the mixture is heated by conduction. In someembodiments, the binder includes a plastic substantially free ofchlorine. In some embodiments, heating the mixture includes increasingthe malleability of the plastic. In some embodiments, heating themixture includes melting or softening the plastic.

In some embodiments, the fuel composition includes the coal distributedin a plastic matrix.

In some embodiments, shaping the fuel composition includes cutting,shredding, or milling the mixture to form discrete portions of the fuelcomposition. In some embodiments, the mixture is extruded to yield anextruded fuel product before cutting, shredding, or milling the mixtureof coal and binder. In some embodiments, the extruded fuel productincludes the coal distributed in a plastic matrix.

In some embodiments, the fuel composition includes about 5 wt % to about50 wt % of the binder.

In some embodiments, the mixture is heated to a temperature between 100°C. and 250° C., between 110° C. and 240° C., 120° C. and 230° C.,between 130° C. and 220° C., or between 140° C. and 210° C.

In some embodiments, the coal placed in the vessel is uncrushed.

Certain aspects of the subject matter described can be implemented as afuel composition. The fuel composition includes coal having a heatcontent between about 4,000 BTU/lb and about 8,300 BTU/lb and a binderincluding plastic. The fuel composition includes less than 5 wt % coaldust having an average primary particle size of 75 micrometers orsmaller.

This, and other aspects, can include one or more of the followingfeatures.

In some embodiments, the coal includes lignite.

In some embodiments, the binder is in the form of a plastic matrix. Insome embodiments, the coal is bound in the plastic matrix.

In some embodiments, the fuel composition includes about 5 wt % to about50 wt % of the binder. In some embodiments, the fuel compositionincludes about 5 wt % to about 40 wt % of the binder. In someembodiments, the fuel composition includes about 5 wt % to about 30 wt %of the binder. In some embodiments, the fuel composition includes about5 wt % to about 25 wt % of the binder. In some embodiments, the fuelcomposition includes about 5 wt % to about 20 wt % of the binder. Insome embodiments, the fuel composition includes about 5 wt % to about 15wt % of the binder. In some embodiments, the fuel composition includesabout 5 wt % to about 10 wt % of the binder. In some embodiments, thefuel composition includes about 10 wt % of the binder.

In some embodiments, the fuel composition is in the form of a solidinhomogeneous mixture.

In some embodiments, the plastic includes polyethylene. In someembodiments, the fuel composition includes polyethylene terephthalate.In some embodiments, the plastic is free of chlorine.

In some embodiments, the fuel composition has a moisture content betweenabout 1 wt % and about 3 wt % or between about 2 wt % and about 3 wt %.

In some embodiments, a heat content of the fuel composition is at leastabout 9,000 BTU/lb. In some embodiments, a heat content of the fuelcomposition is at least about 10,000 BTU/lb. In some embodiments, a heatcontent of the fuel composition is between about 10,000 BTU/lb and about11,000 BTU/lb. In some embodiments, a heat content of the fuelcomposition is at least about 1.5, 1.6, 1.7, 1.8, 1.9, or 1.95 timesgreater than the heat content of the coal.

DETAILED DESCRIPTION

“Low rank coal” is a coal typically having a heat content (for example,higher heating value (HHV)) between about 4,000 BTU/lb and about 8,300BTU/lb and a moisture content between about 20 wt % and about 60 wt % orbetween about 40 wt % and about 50 wt %. In some embodiments, low rankcoal has a fixed carbon content between about 30 wt % and about 70 wt %.In some embodiments, low rank coal has an ash content of less than about10 wt %. In some embodiments, low rank coal has a volatiles contentbetween about 5 wt % and about 50 wt %. One example of low rank coal islignite.

Transportation of unprocessed low rank coal can be consideredinefficient due to its high moisture content. In effect, paying totransport unprocessed low rank coal can be considered wastefully payingfor transport of a resource that can be about half water by weight.Thus, it can be beneficial to remove moisture content from low rank coalbefore transportation. Methods to remove the moisture in lignite havebeen employed but entail specific challenges. One such challenge is thatlignite must often be crushed or pulverized as a separate step, prior toeffective moisture removal. For example, in order to remove moisturecontent from low rank coal, the low rank coal needs to be reduced insize (e.g., pulverized) so that the water trapped in the low rank coalcan escape. However, pulverizing the low rank coal in order to reducemoisture content can produce coal dust and can pose handling, logisticsand transport challenges, including due to the creation of dust. Forexample, pulverizing the low rank coal in order to reduce moisturecontent can produce coal dust and can convert the low rank coal into anon-transportable form (e.g., a hazardous powder). Therefore, afterreducing the moisture content of the low rank coal, the low rank coalneeds to be re-packaged and/or processed into a transportable form.

The methods described in this disclosure can be implemented to completethe steps of removing moisture content from low rank coal andre-packaging the low rank coal with reduced moisture content into atransportable form in a single batch process. One example advantage ofthe methods described herein is that the energy content of the coal isincreased on a per weight basis, while also displacing a certainpercentage of coal with a waste material that otherwise would not bebeneficially used, thus allowing for a near-term reduction of the amountof coal needed by the operator due to the higher energy content andreducing the negative environmental impact of coal combustion emissionsand the total demand for coal. As described in this disclosure, in someembodiments, low rank coal is combined with a binder to yield a fuelcomposition including a binder.

Suitable binders include one or more plastics, such as low, medium, andhigh-density polyethylene. Some additional examples of a suitable binderinclude polyethylene terephthalate, polystyrene, polyester, polyamides,acrylonitrile butadiene styrene, polyethylene/acrylonitrile butadienestyrene, polycarbonate, polycarbonate/acrylonitrile butadiene styrene,polyurethanes, maleimide/bismaleimide, melamine formaldehyde, phenolformaldehydes, polyepoxide, polyetheretherketone, polyetherimide,polyimide, polylactic acid, polymethyl methacrylate,polytetrafluoroethylene, urea-formaldehyde, and polypropylene. The fuelcomposition typically includes between 5 wt % and 50 wt % of the binder(e.g., between 5 wt % and 40 wt %, between 5 wt % and 30 wt %, between 5wt % and 25 wt %, between 5 wt % and 20 wt %, between 5 wt % and 15 wt%, or between 5 wt % and 10 wt %). In one example, the fuel compositionincludes about 10 wt % of the binder. The binder is typically free ofchlorine. In some embodiments, the binder is substantially free ofchlorine-containing plastics, such as polyvinyl chloride. The fuelcomposition is in the form of a solid, inhomogeneous mixture (e.g., aplastic matrix, with the coal bound in the plastic matrix). The bindercan be reclaimed from municipal waste or recycling. The binder can beused as is or cut or shredded before it is combined with the coal.

Processing low rank coal includes placing coal having a heat contentbetween about 4,000 BTU/lb and about 8,300 BTU/lb in a vessel. The coalcan be uncrushed (e.g., straight from a mine) or crushed. In some cases(e.g., when the coal is crushed), the binder is combined with the coalbefore heating. In other cases (e.g., when the coal is uncrushed), thecoal is heated prior to addition of the binder. The coal (or coal-bindermixture) can be sealed in the vessel.

The coal (or coal-binder mixture) is heated by conduction. Heating thecoal (or coal-binder mixture) by conduction includes contacting the coal(or coal-binder mixture) with a heated surface. Heating the coal (orcoal-binder mixture) can occur without providing heated gas (e.g., air)to the vessel. In one example, the heated surface includes one or moreblades configured to rotate in the vessel. The coal (or coal-bindermixture) can be heated to a temperature up to about 250° C. In someexamples, the coal (or coal-binder mixture) is heated to a temperaturebetween 100° C. and 250° C., between 110° C. and 240° C., between 120°C. and 230° C., between 130° C. and 220° C., or between 140° C. and 210°C. The heat provided is insufficient to pyrolyze the coal. Moreover, insome embodiments, heated fluid (e.g., in the form of steam or air) isnot provided to the vessel.

When the coal (or coal-binder mixture) is heated by a blade configuredto rotate in the vessel, the blade(s) can be rotated at a speed betweenabout 1 and about 10 rotations per minute. The blade(s) can be rotatedintermittently, such that the blade is stationary at times and in motionat other times. The intermittent rotation can occur in a pattern (e.g.,periodically) or occur randomly. The coal (or coal-binder mixture) canbe agitated (e.g., by rotation of the blade(s)). The agitation can occurintermittently (e.g., during rotation of the blade(s)). In someembodiments, the agitation is intermittently performed in intervals ofabout 1 minute separated by pauses in agitation of about 1 minute toabout 3 minutes. In some embodiments, the blade(s) protrude radiallyoutward from and are coupled to a central rod. In some embodiments, thecentral rod is rotated, for example, by a motor, to rotate the blade(s),resulting in agitation of the coal within the vessel. While the methodsprovided herein can produce fines and/or dust during processing, thefines and/or dust are largely stabilized once the processing has beencompleted to significantly reduce the amount of fines and/or dustby-product that are produced by the system. For example, duringprocessing, the fines and/or dust can be stabilized by either densifyingthe fines and/or dust into a solid fuel product and/or by adding plasticto bind the fines and/or dust together to form the solid fuel product.The pattern, duration, and extent of agitation can be selected to reduceor minimize pulverization of the coal, and thereby reduce or minimizethe amount of fines and/or dust by-product produced from the coal.

In some embodiments, the blade(s) are rotated at a speed that is lessthan 25 revolutions per minute (rpm), less than 20 rpm, less than 15rpm, less than 10 rpm, or less than 5 rpm. In some embodiments, theblade(s) are rotated at a speed between 2 rpm and 25 rpm. In someembodiments, the speed at which the blade(s) are rotated is varied. Insome embodiments, the speed at which the blade(s) are rotated is variedbetween 1 rpm and 25 rpm. In some embodiments, the blades are notrotated at all, or not rotated for a desired time duration (e.g., 1 minto 5 mins). In some embodiments, the speed at which the blade(s) arerotated alternates between gradually decreasing and graduallyincreasing. In some embodiments, the time duration(s) of no rotation ofthe blade(s) is between 1 minute and 3 minutes. In some embodiments, theblade(s) are rotated around a longitudinal axis defined by the centralrod, such that an outermost tip of the blade(s) has a maximum tangentialvelocity of about 20 inches per second (in/s) or about 15 in/s. In someembodiments, the blade(s) are rotated around the longitudinal axisdefined by the central rod, such that the outermost tip of the blade(s)has a tangential velocity between 5 in/s and 15 in/s.

The pressure in the vessel can be reduced to below atmospheric pressure(vacuum). As used in this disclosure, the term “vacuum” can encompassany pressure that is less than atmospheric pressure (1 atmosphere).Reducing the pressure in the vessel can occur intermittently. Theintermittent pressure reduction can occur in a pattern (e.g.,periodically) or occur randomly. That is, the pressure may be reduced,then allowed to increase (e.g., to atmospheric pressure), and thenreduced again. The pressure in the vessel can be reduced to a pressurebetween 10 torr and 150 torr, between 50 torr and 150 torr, or between50 torr and 100 torr. With reduced pressure in the vessel, the coal maybe heated to a temperature between about 30° C. and about 100° C.Reducing the pressure in the vessel (e.g., to about 50 torr) and heatingto a lower temperature (e.g., 40° C.) may yield the same results asheating at a greater pressure (e.g., atmospheric pressure) and a greatertemperature (e.g., 140° C.). Reducing the pressure promotes thermaltransformation, removal of moisture (e.g., in the form of water vapor),and also promotes removal of oxygen, thereby mitigating and/orpreventing ignition of the coal.

Pressure reduction in the vessel can be carried out by using, forexample, a vacuum pump. Reducing pressure in the vessel can involveusing the vacuum pump to evacuate vapor from an interior of the vessel.For example, an outlet of a vapor space of the vessel is connected tothe vacuum pump, and during operation, the vacuum pump pulls vapor fromthe vapor space of the vessel. The outlet of the vapor space of thevessel that is connected to the vacuum pump is located a predetermineddistance away from a processing zone of the vessel that includes therotating blade(s). In some embodiments, the outlet is located at leastone radius away from an outermost tip of the rotating blade(s), in whichthe radius is defined as the distance between the central rod and theoutermost tip of the rotating blade(s). For example, for mixing blade(s)that radially protrude twelve inches from the central rod, the radius istwelve inches, and the outlet is located at least twelve inches awayfrom the outermost tip of the rotating blade(s). In this example, thisalso means that the outlet is located at least 24 inches away from thecentral rod. In some embodiments, the outlet is located at least oneradius away from the outermost tip of the rotating blade(s) and alsoabove the rotating blade(s) with respect to gravity. The orientation ofthe outlet and the distance away from the processing zone (the rotatingblade(s)) can mitigate and/or prevent coal dust from being evacuatedwith the vapor by the vacuum pump. The intermittent agitation can alsomitigate and/or prevent coal dust from being evacuated with the vapor bythe vacuum pump. For example, by pausing the agitation intermittently,coal dust can be allowed to settle via gravity to mitigate and/orprevent coal dust from being evacuated with the vapor by the vacuumpump.

In some embodiments, a knockout pot is included between the outlet andthe vacuum pump for collecting water. In some embodiments, a filter isincluded between the outlet and the vacuum pump for mitigating and/orpreventing particulates from reaching the vacuum pump. In someembodiments, the filter is downstream of the knockout pot. In someembodiments, the filter is a single stage filter. In some embodiments,the filter is a multi-stage filter, such as a dual stage filter or a3-stage filter. For example, the filter is a multi-stage filter having a1^(st) stage filter defining openings with a maximum dimension between30 micrometers and 50 micrometers, a 2^(nd) stage filter definingopenings with a maximum dimension between 10 micrometers and 20micrometers, and a 3^(rd) stage filter defining openings with a maximumdimension between 2 micrometers and 10 micrometers.

Thus, the coal (or coal-binder mixture) is introduced to a singlevessel, and processed by a low speed, mid to high torque mechanicalblending while being exposed to heat (i.e., contacting heated surfaces).Heat and/or vacuum exposure within the vessel can cause the coal to bereduced in size without requiring a time and/or energy-intensive processof mechanically reducing the coal (for example, by smashing or rigorousagitation using substantial force, and/or investing several hours oftime to process). In some cases, the coal is pulverized into finesand/or dust within a short time (e.g., between 5-30 minutes) of beingexposure to heat and vacuum within the vessel. In some embodiments, thecoal is reduced to having an average primary particle size of less than1 millimeter within a predetermined time. As used herein, a “primaryparticle size” refers to the longest linear dimension, e.g., a maximumlength or a maximum diameter, of a primary particle. As used herein, a“primary particle” is an individual single particle, not anagglomeration of two or more particles. In some embodiments, a primaryparticle can be visually identified by microscopy and distinguished fromagglomerations of two or more primary particles based on size, shape, orboth.

In some embodiments, the coal is reduced to having an average primaryparticle size between 1 micrometer and 1 millimeter, between 1micrometer and 500 micrometers, or between 1 micrometer and 100micrometers. In some embodiments, the coal is reduced to having anaverage primary particle size of about or less than 100 micrometers(e.g., or about or less than 90 micrometers, 80 micrometers, 70micrometers, 60 micrometers, 50 micrometers, 40 micrometers, 30micrometers, 20 micrometers, 10 micrometers, 9 micrometers, 8micrometers, 7 micrometers, 6 micrometers, 5 micrometers, 3 micrometers,or 1 micrometer).

In some embodiments, the predetermined time for achieving the desiredaverage primary particle size is about or no more than 5 minutes, 10minutes, 15 minutes, 20 minutes, 25 minutes, 30 minutes, 1 hour, 2hours, or about or no more than 3 hours of being exposed to heat and/orvacuum within the vessel.

In cases in which binder is included, the heat exposure causes thebinder to melt or soften. In some cases, the coal is pre-heated (e.g.,10 to 20 minutes) before addition of the binder. After addition of thebinder, the coal-binder mixture is processed until the binder reaches atemperature of at least 180° C. (e.g., sufficient to melt or soften theplastic). The melted or softened plastic can serve as a binder for thecoal that has been reduced in size from being exposed to heat and vacuumwithin the vessel. The coal or coal-binder mixture (both of which can beconsidered a fuel composition) can be mechanically forced through anextrusion die to yield a shaped fuel composition. The shaped fuelcomposition can be cut, shredded, or milled to form discrete portions ofthe fuel composition. In some cases, the discrete portions can includepellets or briquettes. In some cases, the coal-binder mixture does notundergo extrusion (which can be energy-intensive) and is simply cut,shredded, or milled to form discrete portions of the fuel composition.

The fuel composition has a moisture content of less than 3 wt %, lessthan 2 wt %, or less than 1 wt %, and a heat content of at least about1.5, 1.6, 1.7, 1.8, 1.9, or 1.95 times greater than the heat content ofthe unprocessed coal (e.g., at least about 9,000 BTU/lb, at least about10,000 BTU/lb, or between about 10,000 BTU/lb and about 11,000 BTU/lb).In some embodiments, the fuel composition has a fixed carbon contentbetween about 40 wt % and about 70 wt % or between about 50 wt % andabout 60 wt %. In some embodiments, the fuel composition has an ashcontent between about 5 wt % and 20 wt % or between about 10 wt % andabout 20 wt %. In some embodiments, the fuel composition has a volatilescontent between about 40 wt % and about 70 wt %, between about 40 wt %and about 60 wt %, or between about 40 wt % and about 50 wt %.

In some embodiments, after the fuel composition has been formed, it issubstantially free of coal dust (for example, the composition issubstantially free of coal particulates having an average size of 75micrometers or smaller). The term “substantially free” can refer to thecomposition containing less than 1 wt. % (e.g., less than 0.5 wt. %,less than 0.1 wt. %, less than 0.01 wt. % or less than 0.001 wt. %) of amaterial. In some embodiments, after the fuel composition has beenformed, it comprises less than 20 wt % coal dust, less than 15 wt % coaldust, less than 10 wt % coal dust, less than 5 wt % coal dust, less than4 wt % coal dust, less than 3 wt % coal dust, less than 2 wt % coaldust, less than 1 wt % coal dust, less than 0.5 wt % coal dust, or lessthan 0.1 wt % coal dust. In some embodiments, after the fuel compositionhas been formed, it is substantially free of coal dust. In someembodiments, after the fuel composition has been formed, it releasesless than 20 wt % coal dust, less than 15 wt % coal dust, less than 10wt % coal dust, less than 5 wt % coal dust, less than 4 wt % coal dust,less than 3 wt % coal dust, less than 2 wt % coal dust, less than 1 wt %coal dust, less than 0.5 wt % coal dust, or less than 0.1 wt % coaldust.

The methods described herein can be implemented to convert unprocessed,uncrushed low rank coal into the fuel composition provided herein within1 hour, within 55 minutes, within 50 minutes, within 45 minutes, within40 minutes, within 35 minutes, within 30 minutes, within 25 minutes, orwithin 20 minutes.

Example

Uncrushed lignite coal taken directly from a Mississippi mine showedtypical characteristics: 43.22 wt % moisture, 26.4 wt % volatiles, HHVof 5922 BTU/lb, 0.012 wt % sulfur, and 6.63 wt % ash. The composition ofthe uncrushed and unprocessed lignite coal is provided in Table 1.

TABLE 1 Composition of uncrushed lignite coal Component Amount (wt %)Moisture 43.22 Carbon 34.96 Hydrogen 2.71 Nitrogen 0.65 Sulfur 0.012 Ash6.63 Oxygen 11.82

The coal was exposed to heat ranging from 140-208° C. for a duration ofapproximately 60 minutes. The mechanism of heat transfer was conduction.Slow speed (up to 25 rpm), high torque mechanical blades were used topromote intermittent contact with the lignite, and a careful balance wasmaintained to reduce creation of coal dust. The mechanical blades wererotated intermittently, and the rotation speed varied between 0 rpm and25 rpm with gradual increases and decreases. The rotation of themechanical blades was paused (that is, no rotation) for time durationsof between 1 minute and 2 minutes. The coal was kept in a vessel at alltimes, with intermittent exposure to vacuum. The vacuum was introduced(1) to remove oxygen and, thus, reduces the likelihood of ignition ofthe coal and (2) to promote thermal transformation. The pressure withinthe processing chamber, at various points during processing, was kept at150 torr or less. The combination of heat and slow speed intermittentmechanical processing facilitated a natural breakdown of the coal.

10 wt % plastic (a blend of high-density polyethylene, low-densitypolyethylene, and polyethylene terephthalate) was combined with the coalafter the coal had been preheated, by introducing the plastic betweenthe 10 and 20 minute time intervals. Samples 1 and 2 were the resultingfuel compositions after the coal was processed and combined with theplastic. In Sample 1, the coal and plastic mixture was extruded. InSample 2, the coal and plastic mixture was not extruded. Processing ofthe lignite resulted in a moisture reduction from 43.22 wt % to lessthan 3 wt % (2.46 wt % and 1.43 wt % for Samples 1 and 2, respectively)and an increase in energy content from 5,922 BTU/lb to 10,649 and 10,285BTU/lb (HHV) for Samples 1 and 2, respectively. The compositions ofSamples 1 and 2 are provided in Table 2.

TABLE 2 Composition of Samples 1 and 2 Sample 1 Sample 2 (extruded) (notextruded) Component Amount (wt %) Moisture 2.46 1.43 Carbon 58.95 58.23Hydrogen 5.02 4.83 Nitrogen 0.97 1.01 Sulfur 0.352 0.412 Ash 13.64 14.76Oxygen 18.61 19.33

As used in this disclosure, the terms “a,” “an,” or “the” are used toinclude one or more than one unless the context clearly dictatesotherwise. The term “or” is used to refer to a nonexclusive “or” unlessotherwise indicated. The statement “at least one of A and B” has thesame meaning as “A, B, or A and B.” In addition, it is to be understoodthat the phraseology or terminology employed in this disclosure, and nototherwise defined, is for the purpose of description only and not oflimitation. Any use of section headings is intended to aid reading ofthe document and is not to be interpreted as limiting; information thatis relevant to a section heading may occur within or outside of thatparticular section.

As used in this disclosure, the term “about” or “approximately” canallow for a degree of variability in a value or range, for example,within 10%, within 5%, or within 1% of a stated value or of a statedlimit of a range.

As used in this disclosure, the term “substantially” refers to amajority of, or mostly, as in at least about 50%, 60%, 70%, 80%, 90%,95%, 96%, 97%, 98%, 99%, 99.5%, 99.9%, 99.99%, or at least about 99.999%or more.

Values expressed in a range format should be interpreted in a flexiblemanner to include not only the numerical values explicitly recited asthe limits of the range, but also to include all the individualnumerical values or sub-ranges encompassed within that range as if eachnumerical value and sub-range is explicitly recited. For example, arange of “between 0.1% and about 5%” or “between 0.1% and 5%” should beinterpreted to include about 0.1% to about 5%, as well as the individualvalues (for example, 1%, 2%, 3%, and 4%) and the sub-ranges (forexample, between 0.1% and 0.5%, between 1.1% and 2.2%, and between 3.3%and 4.4%) within the indicated range. The statements “X to Y” and“between X and Y” have the same meanings as “about X to about Y” and“between about X and about Y”, unless indicated otherwise. Likewise, thestatement “X, Y, or Z” has the same meaning as “about X, about Y, orabout Z,” unless indicated otherwise.

The details of one or more embodiments of the subject matter of thisdisclosure are set forth in the accompanying drawings and thedescription. Other features, aspects, and advantages of the subjectmatter will become apparent from the description, the drawings, and theclaims.

Although this disclosure contains many specific embodiment details,these should not be construed as limitations on the scope of the subjectmatter or on the scope of what may be claimed, but rather asdescriptions of features that may be specific to particular embodiments.Certain features that are described in this disclosure in the context ofseparate embodiments can also be implemented, in combination, in asingle embodiment. Conversely, various features that are described inthe context of a single embodiment can also be implemented in multipleembodiments, separately, or in any suitable sub-combination. Moreover,although previously described features may be described as acting incertain combinations and even initially claimed as such, one or morefeatures from a claimed combination can, in some cases, be excised fromthe combination, and the claimed combination may be directed to asub-combination or variation of a sub-combination.

Particular embodiments of the subject matter have been described. Otherembodiments, alterations, and permutations of the described embodimentsare within the scope of the following claims as will be apparent tothose skilled in the art. While operations are depicted in the drawingsor claims in a particular order, this should not be understood asrequiring that such operations be performed in the particular ordershown or in sequential order, or that all illustrated operations beperformed (some operations may be considered optional), to achievedesirable results.

Accordingly, the previously described example embodiments do not defineor constrain this disclosure. Other changes, substitutions, andalterations are also possible without departing from the spirit andscope of this disclosure.

What is claimed is:
 1. A method of preparing a fuel composition, themethod comprising: placing coal having a heat content between about3,000 BTU/lb and about 9,000 BTU/lb and a moisture content in a rangebetween about 20 wt % and about 60 wt % in a vessel; exposing the coalto heat and a pressure less than atmospheric pressure within the vessel,thereby reducing the coal, such that an average primary particle size ofthe coal is less than 1 millimeter; introducing a binder to the vessel,such that the coal combines with the binder to yield a mixture; andshaping the mixture to yield a fuel composition.